This application claims the benefit of Korean Application No. 2002-7027, filed Feb. 7, 2002, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a wet color image forming apparatus and a method of forming an image using the same, and more particularly, to a wet color image forming apparatus to transfer a color image using electrostatic force and pressure which is capable of increasing efficiency when transferring the image from a transfer belt to a paper, and a method of forming an image using the same.
2. Description of the Related Art
A wet color image forming apparatus using a developing solution, e.g., a printer, can obtain a high quality image because efficiency when transferring an image from a transfer belt to a paper is high, as compared to a dry image forming apparatus using toner.
FIG. 1 is a cross-sectional view of a wet color image forming apparatus according to the related art. Referring to FIG. 1, the wet color image forming apparatus includes a photosensitive body portion P1, a developing apparatus portion P2, and a transfer portion P3. Paper supplying and paper discharging portions are further included, and a developing cartridge (not shown) to supply a developing solution to the developing apparatus portion P2 is further included under the developing apparatus portion P2.
The photosensitive body portion P1 includes first through fourth photosensitive bodies 40, 42, 44, and 46 that are spaced apart from each other. The first through fourth photosensitive bodies 40, 42, 44, and 46 are black (BK), cyan (C), magenta (M), and yellow (Y), respectively, on which latent electrostatic images of different colors are formed. A latent electrostatic image corresponding to a black image is formed on the black (BK) photosensitive body 40. A latent electrostatic image corresponding to a cyan image is formed on the cyan (C) photosensitive body 42. A latent electrostatic image corresponding to a magenta image is formed on the magenta (M) photosensitive body 44. A latent electrostatic image corresponding to a yellow image is formed on the yellow (Y) photosensitive body 46. Reference numerals 50, 52, 54, and 56 are first through fourth cleaning blades, which contact and clean the first through fourth photosensitive bodies 40, 42, 44, and 46, respectively. Erasers, chargers, and light scanning units (not shown) are further installed around the first through fourth photosensitive bodies 40, 42, 44, and 46. The erasers neutralize the photosensitive bodies 40, 42, 44, and 46 which are charged after developed latent electrostatic images are transferred. The chargers re-charge the neutralized surfaces of the photosensitive bodies 40, 42, 44, and 46 before latent electrostatic images are formed. The laser scanning units radiate light onto the re-charged surfaces of the photosensitive bodies 40, 42, 44, and 46 to form the latent electrostatic images.
The developing apparatus portion P2 under the photosensitive body portion P1 includes first through fourth developer units 60, 62, 64, and 66 which are opposite the first through fourth photosensitive bodies 40, 42, 44, and 46, respectively, and supply color developing solutions, i.e., ink, necessary to develop the latent electrostatic images formed on the first through fourth photosensitive bodies 40, 42, 44, and 46. Reference numerals 60a, 62a, 64a, and 66a are first through fourth developer rollers which contact and supply the first through fourth photosensitive bodies 40, 42, 44, and 46 with color developing solutions, respectively.
The transfer portion P3 includes a transfer belt 70 to which a predetermined color image is transferred. The predetermined color image is formed by overlapping resultant materials developed on the first through fourth photosensitive bodies 40, 42, 44, and 46 on a predetermined portion of the transfer belt. The transfer belt 70 is formed of polyimide and has a hardness of 70 (Shore A) or more. The transfer belt 70 has first, second, fourth, fifth, sixth and seventh rollers 72, 74, 78, 80, 82, and 84 therein. A third roller 76 is prepared outside the transfer belt 70 opposite the first roller 72. Except for the third roller 76, the first, second, fourth, fifth, sixth and seventh rollers 72, 74, 78, 80, 82, and 84 maintain the transfer belt 70 in a form suitable for the image transfer. The third roller 76 is grounded and is a paper transfer roller which transfers the color image on the transfer belt 70 to a paper P. The third roller 76 has a hardness of about 30 (Shore A) and causes a cushioning effect. The first roller 72 is a paper transfer backup roller to back up the third roller 76 and is formed of a rubber material having a hardness of about 50 (Shore A). A fifth power supply S5 applies a voltage to generate an electrostatic force to the first roller 72 when starting the image transfer. The fourth through seventh rollers 78, 80, 82, and 84 are first through fourth transfer backup rollers, respectively, which are used to transfer images on the first through fourth photosensitive bodies 40, 42, 44, and 46 to the transfer belt 70. Since the images on the first through fourth photosensitive bodies 40, 42, 44, and 46 are charged, the fourth through seventh rollers 78, 80, 82, and 84 must be charged in a charge state, which is opposite to the charge state of the images . This is done to transfer the images to the transfer belt 70. First through fourth power supplies S1, S2, S3, and S4 supply the charge to the fourth through seventh rollers 78, 80, 82, and 84, respectively. The second roller 74 is a driver roller to drive the transfer belt 70 to form the color image by overlapping the resultant materials developed on the photosensitive bodies 40, 42, 44, and 46 accurately and to transfer the color image from the transfer belt 70 accurately to the paper P.
In the wet color image forming apparatus, the color image on the transfer belt 70 is transferred to the paper P by a pressure between the third roller 76 and the transfer belt 70 and an electrostatic force generated by the voltage applied to the first roller 72. The force applied to the entire contact surface between the third roller 76 and the transfer belt 70 is about 3 kg. Since such a low pressure is used, the transfer is achieved only by the electrostatic force. In this case, a large amount of the developing solution is not transferred and remains on the transfer belt 70 after the transfer. This remaining developing solution is thrown away, which increases the amount of unnecessarily consumed developing solution. This problem is solved by reducing the amount of developing solution supplied to the transfer belt 70 during the development. However, in this case, the density of the color image transferred from the transfer belt 70 to the paper P is degraded. As a result, there has been suggested a wet color image forming apparatus which applies a force of 70 Kg or more between the third roller 76 and the first roller 72 to hot-press the paper P so that the color image is transferred to the paper P. If this wet color image forming apparatus is used, the total amount of unused developing solution is reduced as compared to the wet color image forming apparatus using only electrostatic force. However, it is difficult to clean the developing solution. Thus, after cleaning the developing solution, the developing solution remains on the surface of the transfer belt, which shortens the usable period of the transfer belt.
Accordingly, it is an object of the present invention to provide a wet color image forming apparatus which is capable of increasing efficiency when transferring a color image from a transfer belt to a paper without shortening the usable period of the transfer belt from being shortened.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the dexc5x9cription, or may be learned by practice of the invention.
It is another object of the present invention to provide a method of forming an image using the wet color image forming apparatus.
The foregoing and other objects of the present invention are achieved by providing a wet color image forming apparatus, to form a multi-colored image on a paper including a plurality of photosensitive bodies which form a plurality of latent electrostatic images thereon corresponding to image information input from an outside; a plurality of developing units to develop the latent electrostatic images; a transfer belt on which the developed electrostatic images are overlapped to form the multi-colored image thereon; a paper transfer roller by which the multi-colored image on the transfer belt is transferred to the paper; and a multi-function roller to drive the transfer belt and to support the paper transfer roller during the transfer of the image to the paper, wherein the transfer belt includes a surface layer to contact the photosensitive bodies and the paper transfer roller, a first cushion layer that contacts the multi-function roller, and a second cushion layer interposed between the surface layer and the first cushion layer and having a lower hardness than a hardness of the first cushion layer.
According to an aspect of the present invention, the first and second cushion layers are first and second urethane layers, respectively, which have hardnesses of 80 and 50 (Shore A), respectively.
According to an aspect of the present invention, the paper transfer roller has a hardness of about 40-50 (Shore A). The multi-function roller may be a solid roller having no cushion which is formed of stainless steel or aluminum and may be connected to a power supply that supplies a voltage of about 2.4-3.2 kV. The multi-function roller may apply a force of 40 kg or more to the entire contact surface between the multi-function roller and the paper transfer roller during the transfer of the image.
The foregoing and other objects of the present invention are also achieved by providing a method of forming an image using a wet color image forming apparatus. According to the method, a voltage of 2.4-3.2 kV is applied to the multi-function roller while a force of 40 kg or more is applied to the entire contact surface between a paper transfer roller and a multi-function roller during the transfer of the image.
According to an aspect of the present invention, the transfer belt includes a surface layer to contact the photosensitive bodies and the paper transfer roller; a first cushion layer to contact the multi-function roller; and a second cushion layer interposed between the surface layer and the first cushion layer and having a lower hardness than a hardness of the first cushion layer. The first and second cushion layers may be formed of first and second urethane layers, respectively.
Using the wet color image forming apparatus and the method of forming an image using the wet color image forming apparatus, an efficiency when transferring a color image from a transfer belt to a paper is increased. Thus, the amount of ink remaining on the transfer belt after transferring the color image is extremely small and the transfer belt does not need to be supplied with additional ink. Moreover, since the amount of ink remaining on the transfer belt is extremely small, the usable period of the transfer belt is increased. In other words, a high quality image can be transferred to the paper using only the minimum amount of ink necessary for the transfer and the usable period of the transfer belt is thereby increased.